Digital interferometric and holographic imaging is a quantitative optical imaging technique, which is able to capture the complex wave-front (amplitude and phase) of the light interacted with a sample. This is performed by recording a spatial interference pattern of the beam interacted with the sample and a mutually-coherent reference beam using a digital camera. Digital interferometric and holographic imaging affected many fields of science, and one of them, is digital interferometric phase microscopy (IPM), also called digital holographic microscopy. IPM is a label-free quantitative tool for capturing the complex wave-front of transparent or translucent microscopic samples and processing it into the spatial optical thickness maps of the samples. This tool is useful for a wide range of applications, including biological cell imaging and nondestructive quality tests of optical elements [1,2].
Although it is easier to obtain interference with a highly coherent source, using such a source in interferometric and holographic imaging in general and in IPM in particular significantly reduces the image quality due to parasitic interferences and coherent noises. To overcome this problem, low-coherence light sources are employed. However, to obtain interference with these sources, meticulous alignment between the optical paths of the two beams is required. For off-axis interferometric geometry, which enables a single-exposure acquisition mode, the sample and the reference beams interfere on the digital camera with a small angle, so even with strict alignment between the beam optical paths, it is frequently not possible to obtain interference on the entire camera field of view (FOV), due to the angular beam-path difference inside the beam cross section, which might be above the coherence length of the source. The practical meaning of this limitation is that large samples cannot be simultaneously recorded by off-axis interferometry on the entire camera sensor using low-coherence sources. Diffractive gratings can solve this problem by tilting the field of the beams to be in plane, with the cost of possible aliasing and image modulation.
Even if using a highly coherent source, where the off-axis interference is obtained on the entire camera sensor, many interferometric setups are subjected to a small FOV of acquisition, as the size of the camera sensor used for the digital recording of the interferogram is smaller than the optical FOV defined by the microscope objective aperture projected onto the camera plane. This narrow camera-FOV restriction is especially critical when imaging large samples with fine details in high magnifications or when imaging dynamics of objects which might move out of the camera FOV.